'06 LX470 AHC Issues – 0 pressure, stuck in N, won't raise/lower

[dim06]

Hi all,

A week or so ago I replaced the globes+fluid on my '06 LX470. After replacing the globes I mistimed a reservoir refill, the tank drew down to empty, and the AHC switched itself "OFF". I topped up, restarted the car, and was pleased to find that fluid drew down into the system, the car equalized, and I could move between L/N/H with ease — and I had 12 gradations on the side! The ride was much smoother, and I figured all was good to go.

However, over the next few days I found I had trouble moving through L/N/H — it would take a very long time to do anything. Eventually I landed back at N, and now if I try to raise or lower, the light will flash forever, and the car will not raise/lower. I can (sometimes) hear a stuttering sound, not from the pump but more from under the car.

I ran techstream to take a look and was not able to engage the motor/pump – it would switch to OFF and stay there. I had error code, C1763 - "Oil pressure for pump motor abnormal." Cleared that, tried to engage again, same thing. The code didn't reappear but I'm still unable to engage anything. All of my pressure values were flat 0.0, too.

I'm sure there's air trapped somewhere. I want to bleed the system, but am afraid that I'll drain down to L and then the pump will continue not to engage, and I'll be stuck down there.
From reading around I also suspect my pump attenuator might have the suspected air, and I'll need to bleed that... but I can't find a clear description of how to do this.

Any ideas here?

 

[suprarx7nut]

I see two options.

1. Bleed it and risk getting stuck in L while you figure it out.
2. Don't bleed it and just drive as is for now. Perhaps it just needs to cycle a few times.

No idea if this might work, but I wonder if you start the car and then jack up the front or rear diff a bit, will the system release fluid back to the reservoir and perhaps carry the bubbles with it?

 

[dim06]

I see two options.

1. Bleed it and risk getting stuck in L while you figure it out.
2. Don't bleed it and just drive as is for now. Perhaps it just needs to cycle a few times.

No idea if this might work, but I wonder if you start the car and then jack up the front or rear diff a bit, will the system release fluid back to the reservoir and perhaps carry the bubbles with it?

Thanks for weighing in! I'm going to try a small bleed at first all around, and see if the pump engages when the car restarts. If it doesn't, I don't think I want to bleed all the way down to L.
As for 2. I've probably put 100miles on it since it stopped engaging.

Will try the jack option... Good call.

 

[baltistyle]

Consider pressure bleeding the system as well because this will force the air bubble through and keep fluid in the system. If you connect this with a vacuum pump on one of the bleed nipples, it would ensure a very fast process.

 

[dim06]

Consider pressure bleeding the system as well because this will force the air bubble through and keep fluid in the system. If you connect this with a vacuum pump on one of the bleed nipples, it would ensure a very fast process.

For clarification, would I just need a vacuum pump on one bleeder screw for a pressure bleed, or would I need something "pushing" from the reservoir side, too?

I'm a bit confused as to why it never switches "OFF" or into some sort of failsafe mode when I try to engage L or H. Just flashes eternally...

 

[baltistyle]

For clarification, would I just need a vacuum pump on one bleeder screw for a pressure bleed, or would I need something "pushing" from the reservoir side, too?

I'm a bit confused as to why it never switches "OFF" or into some sort of failsafe mode when I try to engage L or H. Just flashes eternally...

Pushing with fluid is the better option. It really depends where the bubble is, but it’s likely up near the pump. You could also try pulling vacuum on the whole system as well from the reservoir. Just don’t keep running it until this gets fixed because you can burn out the pump.

 

[dim06]

Pushing with fluid is the better option. It really depends where the bubble is, but it’s likely up near the pump. You could also try pulling vacuum on the whole system as well from the reservoir. Just don’t keep running it until this gets fixed because you can burn out the pump.

Sorry for ignorance here but what would "pushing with fluid" look like? Where would I attach ?

 

[baltistyle]

The reservoir.

I’m just listing the options and the concepts. If the bubble is up near the pump, vacuum bleeding from the reservoir might get it out the most quickly.

If the bubble is somewhere down below, which it is likely not because otherwise the pump would work, I would push the fluid from the reservoir, just like a brake bleed with a power bleeder.

Adding a vacuum bleeder at the nipple, pulls the fluid through, not the same concept as a vacuum leader on the reservoir.

It’s a difficult situation that not many people get into and people have a hard time solving, but I’ve had to go through this on other vehicles with hydraulic suspension as well so it’s really just about thinking about the tools that exist to remove bubbles from hydraulic fluid and the concepts are all the same.

And obviously cycle the button
while this is going on.

 

[dim06]

SOLVED! Had some time before Thxgiving cooking and went down another rabbit hole. I wasn't convinced my Techstream thing was actually activating Active Test so I stripped some speaker-wire and got in that way. I had the flashing OFF light, and I held UP, but the car did not raise – instead the car went down to LO, which confused me. I killed the engine, unplugged the motor for no good reason, plugged it back in, left her in LO and went inside.

Then I did some more reading and, for the first time, realized that the pump will only engage if the doors are closed... I had been keeping the door open so I could jump out quickly and check for minor changes in height. Hopped in and took her for a slow drive around the block to reset. Pulled over, kept the doors closed, foot off the brake, and was able to go up to N. Cycled H/N/L with no issues, and with good speed.

I plan to refill and bleed a couple more times to be safe.

Phew!

 

[x8o8drifter]

realized that the pump will only engage if the doors are closed...

Did the same when I first got mine this year and I was checking my pressures.
Same reason too.

 

[baltistyle]

Glad you got it sorted out. Yes that is a thing and many of us have done at some point or another freaking out that the system failed.